This invention relates to a regenerable filter for the exhaust gases of an internal-combustion engine. In particular, this invention relates to a filter suited to be placed into an exhaust pipe of an internal-combustion engine, comprising a filtering member suited to intercept the residual combustion products contained in the exhaust gases and further comprising means suited to produce the combustion of said residues.
Filters are known in which said means suited to produce the combustion of the residues are of the kind that uses a catalyst for the starting of the combustion at low temperatures, or of the kind that heats the exhaust gases, upstream of the filtering member, to the combustion temperature of said residues.
Said filters suffer from certain drawbacks.
In the case of the entirely catalytic filters, it is not uncommon the so-called "poisoning" of the catalyst, due to the presence in the exhaust gases of chemicals that impair their catalytic activity to the point of completely discontinue the combustion of the residues; this originates a gradual clogging of the filter, with the resulting attainement of an unacceptable back-pressure on the engine exhaust.
In the case of heating filters, the heating of the exhaust gases usually takes place by means of resistive elements positioned upstream of the filtering member, which, supplied with an electric current, generate thermal power through Joule effect and rise the temperature of the gases that affect then the filtering surface. This solution entails a high consumption of electric power, with the risk of extreme charge losses of the vehicle battery.
A further drawback of the known heating filters is the fact that the filter temperature can increase exceedingly, since the regeneration usually takes place upon rather wide surfaces and so in a scarcely controlled manner; as a result there is the possibility of serious damages or the destruction due to exaggerated heatings.
For the double object of limiting the average temperature of the filter and reducing the electric power used, filters have been realized in which the filtering member is cyclically heated in relation with consecutive portions; the continuity of the filtering member nevertheless can allow the starting of wide and intense combustions. Furthermore, since in the known filters of this kind the heating of the consecutive portions of the filtering member is obtained through convection and radiation, the electric power overall supplied, is always substantially higher than the equivalent of the thermal power actually needed to locally start the combustion of the residues.
Solutions in which diesel oil or other fuel burners in substitution for said resistive elements are used, are also known; said solutions have however high costs and dimensions together with said problems connected with the regeneration.